A teeth disk comprises one surface of the teeth disk having a plurality of recesses which do not penetrate through the teeth disk; and a bottom of each recess is formed as a stop. Each recess has a cambered shape which is arranged near an edge of the teeth disk. A plurality of teeth are formed along the edge of the teeth disk for engaging to a chain of a bicycle. The teeth disk has a ring structure with a hollow central hole for installing a crank. An inner edge of the central hole is protruded with a plurality of ears; and each ear has an ear hole for combining with a crank.